ci: Add script to repackage WiX .NET tool for our needs

WiX Toolset 4+ is provided only via nuget packages.  Add a script to
repackage the parts we need for CMake's own testing and packaging.

.gitlab/ci/repackage/wix.ps1

@@ -0,0 +1,55 @@
+# WiX Toolset 4+ is provided only via nuget packages.
+# Download the package artifacts, extract the parts we need, and repackage them.
+
+param (
+  [Parameter(Mandatory=$true)]
+  [string]$version
+  )
+
+$erroractionpreference = "stop"
+
+$version_major = $version.Substring(0, $version.IndexOf('.'))
+
+$release = "v" + $version
+$pkg_wix = "wix.$version.nupkg"
+$pkg_wixui = "WixToolset.UI.wixext.$version.nupkg"
+$packages = $pkg_wix, $pkg_wixui
+
+$wix_artifacts = "wix-artifacts.zip"
+
+$ProgressPreference = 'SilentlyContinue'
+Invoke-WebRequest -Uri "https://github.com/wixtoolset/wix/releases/download/$release/artifacts.zip" -OutFile "$wix_artifacts"
+
+Add-Type -AssemblyName System.IO.Compression.FileSystem
+
+$zip = [System.IO.Compression.ZipFile]::Open("$wix_artifacts", "read")
+$zip.Entries | Where-Object FullName -in $packages | ForEach-Object {
+  [System.IO.Compression.ZipFileExtensions]::ExtractToFile($_, "$($_.Name)", $true)
+}
+$zip.Dispose()
+Remove-Item "$wix_artifacts"
+
+$wix_dir = "wix-$version-win-any-1"
+[System.IO.Compression.ZipFile]::ExtractToDirectory($pkg_wix, "wix-tmp")
+Move-Item -Path "wix-tmp/tools/net6.0/any" -Destination "$wix_dir"
+Remove-Item "wix-tmp" -Recurse -Force
+Remove-Item "$pkg_wix"
+
+$ext_dir = New-Item -Force -ItemType Directory -Path "$wix_dir/.wix/extensions/WixToolset.UI.wixext/$version/wixext$version_major"
+$zip = [System.IO.Compression.ZipFile]::Open($pkg_wixui, "read")
+$zip.Entries | Where-Object Name -eq "WixToolset.UI.wixext.dll" | ForEach-Object {
+  [System.IO.Compression.ZipFileExtensions]::ExtractToFile($_, (Join-Path $ext_dir $_.Name), $true)
+}
+$zip.Dispose()
+Remove-Item "$pkg_wixui"
+
+@"
+This was extracted from WiX Toolset nuget packages and repackaged.
+Point both PATH and WIX_EXTENSIONS environment variables at this directory.
+
+"@ | Add-Content -NoNewline "$wix_dir/README.txt"
+
+$compressionLevel = [System.IO.Compression.CompressionLevel]::Optimal
+$includeBaseDirectory = $true
+[System.IO.Compression.ZipFile]::CreateFromDirectory("$wix_dir", "$wix_dir.zip", $compressionLevel, $includeBaseDirectory)
+Remove-Item "$wix_dir" -Recurse -Force